Evaluation of the 5-French saline paediatric gastric tonometer

Abstract

Objective: To evaluate the paediatric 5-French (Fr) saline-filled gastric tonometer. Design: (a) In vitro comparison of saline bath reference pCO₂ with tonometric pCO₂ measured by normal saline-filled and phosphate-buffered saline-filled 5-Fr tonometers, and by a recirculating gas tonometer. ( b) In vivo comparison of gastric intramucosal pCO₂i, measured by normal saline-filled 5-Fr tonometer (NST) and simultaneously by recirculating gas tonometer (RGT) in ten paediatric intensive care patients. (c) In vivo comparison of pCO₂i measured simultaneously by 2 NST 5-Fr tonometers, before and after enteral feeding, in ten paediatric intensive care patients. Measurements and main results: (a) Twenty consecutive measurements of pCO₂ were made at constant reference pCO₂ of 19, 38, 56, and 75 mmHg (2.5, 5.0, 7.5, and 10.0 kPa), respectively. The NST tonometer underestimated reference pCO₂ by mean bias (limits of agreement) of 58 % (20 %), and the phosphate-buffered saline-filled tonometer by 6 % (26 %). The RGT showed mean bias 5.7 % with narrow limits of agreement (1.5 %). (b) In 50 paired (NST vs. RGT) in vivo measurements over pCO₂i range 23–73 mmHg (3.0–9.7 kPa), the NST underestimated RGT pCO₂i by a mean bias of 10 mmHg (1.3 kPa), with limits of agreement + /–10 mmHg (1.5 kPa). This resulted in NST consistently overestimating pHi and underestimating pCO₂ gap (both P < 0.001). (c) One hundred simultaneous paired NST measurements were assessed (50 without, and 50 with enteral feeding). The mean biases (limits of agreement) were identical in the fasted and fed states 0.4 ± 6 mmHg, with no difference between the fed and fasting states (P = 0.7). Conclusions: There are inherent problems in the methodology of saline tonometry, which adversely affect the accuracy and reliability of the 5-Fr paediatric gastric tonometer in comparison to recirculating gas tonometry.